Who else can Dark Samus fight against tho? Or... How many Metroid characters are notably requested into Death Battle?
Samus for a runback is pretty popular, Dark Samus could be used, Ridley is the very popular next option.
Not much else outside of that, though.
The more important question is: which Kirby characters are they more likely bringing into Death Battle? Like said before...
We have had Meta Knight and Bandana Waddle Dee and Galacta Knight and Zero and Zero-Two and Marx and Magolor and Hyness and even Void Termina before Fecto Elfilis. (I know there are more but I am as well bringing the whole list)
Frankly I don't see them utilizing any of the one off villains or major deities such as Hyness, Void Termina, or Fecto Elfilis, as cool as those last two are. As awesome as having a type of fight with the entire Dark Matter species of DM, Zero & Zero Two against someone would be, that's not happening either.
Meta Knight, BanDee, Galacta Knight, Kirby for a runback, and Marx are the only ones I see having the likelihood of showing up. Meta Knight and BanDee are both major playable characters, with MK being a franchise constant since the second game, and BanDee taking several playable P2 roles in multiple games, Galacta Knight was the franchises' consistent superboss for years and is pretty popular within the community and has a variety of various MUs, Kirby as a runback is requested occasionally, and Marx is probably the only one-time villain I can see being popular enough to be used.
Meta Knight is going to fight Zero definitely.
BanDee could fight Hero Prinny from Disgaea
Marx could fight Flandre Scarlet from Touhou
Kirby's most popular runback options are Mario and Rimuru, though I think Yuuma Toutetsu from Touhou is his best MU left. Kirby doesn't rlly need to come back for DB though.
Galacta Knight has way too many options, with no specific definitive "oh it HAS to be this guy" though. I've heard Bardock, Boros, Infinite, Ghidora, Deoxys, Omega, and Gallantmon all brought up but he doesn't have a defined strong choice to my knowledge.